In the field of supplying power for operating equipment, a voltage or potential source is generally provided that is sufficient to drive a given or known load or loads under variable conditions. In this respect, the actual load to be driven may vary due to operating characteristics or other parameters peculiar to the equipment and the results may be somewhat erratic or the operation may not be as smooth as desired.
In certain cases a variation in the supply voltage of as much as 15% above or below the nominal voltage may be realized and therefore the requirement for regulating or compensating for such variation is extremely important in providing for optimum operation. For example, in the specific case of driving print wires in printing operation, it is known that the effects of variations in the operating voltage on impact force and print quality range from illegible or skipped print dots under a low voltage condition to embossment or perforation of the record media under a high voltage condition.
One form of voltage compensation used in prior equipment has included means for detecting the voltage level and, depending upon a range within which the level occurs or falls, causing the proper associated pulse width to be selected from an available range to provide the proper operating voltage. While this form of compensation has been successful for accomplishing certain desired results, the enabling equipment has operated at reduced processing capacity and thus increased the costs of operation.
Representative documentation in the area of providing control of operating voltages includes U.S. Pat. No. 3,634,751, issued to S. A. Miller on Jan. 11, 1972, which discloses a voltage regulator having an operational amplifier and a plurality of constant and variable resistive means such as resistors and zener diodes, respectively. The output of the operational amplifier is coupled to both its positive and negative inputs such that the voltage across the terminal of one of the temperature compensated zener diodes is regulated and is stable with respect to time, temperature and load.
U.S. Pat. No. 3,760,192, issued to J. O. G. Darrow on Sept. 18, 1973, discloses a failsafe level detector including an amplifier and a zener diode in the circuit and wherein the zener diode is used as a signal path for an applied signal to the amplifier when the level is correct and is used to block the signal path when the applied signal level is incorrect.
U.S. Pat. No. 3,829,717, issued to C. E. Harrison on Aug. 13, 1974, discloses reference voltage compensation for a zener diode output voltage in a regulation circuit which uses a resistive voltage divider in parallel with and connecting the zener diode cathode to the negative voltage supply. The anode of the zener diode is connected with a compensating resistor to cause the voltage across the load to remain constant as a result of changing the positive voltage.
U.S. Pat. No. 3,946,302, issued to A. W. Kovalick et al. on Mar. 23, 1976, discloses a method and circuit for providing regulated power by controlling the duty cycle of a fixed frequency signal as a function of the amplitude of an applied voltage and utilizing a comparator along with resistors, capacitors and a zener diode in such circuit.
U.S. Pat. No. 4,237,405, issued to J. T. Kellis on Dec. 2, 1980, discloses a regulating circuit which includes a zener diode for maintaining a constant voltage at a common resistor junction of a fixed reference voltage source.
And, U.S. Pat. No. 4,290,005, issued to R. Arumugham on Sept. 15, 1981, discloses a compensated reference voltage source in a circuit that includes a first resistor, a zener diode and a second resistor connected in series between an operating voltage source and a point of fixed potential all in an arrangement for maintaining a stable voltage at the output terminal of the circuit which is equal to the voltage across the zener diode and remains constant despite variations in operating voltage.